Tell the Difference

2015 National Building Code

9.10.4.4. Roof-Top Enclosures

1) Roof-top enclosures provided for elevator machinery, stairways or service rooms, used for no purpose other than for service to the building, shall not be considered as a storey in calculating the building height.

2018 BC Building Code

9.10.4.4. Roof-Top Enclosures

1) A roof-top enclosure shall not be considered as a storey in calculating the building height if the roof-top enclosure is provided for

a) elevator machinery,

b) a service room,

c) a stairway used for no purpose other than for access or egress,

d) an elevator lobby used for no purpose other than for access or egress, or

e) a combination thereof

The difference is:

If you are designing a 3 storey townhouse with a roof top patio and stairway, it will be 3 storey in BC, but 4 storey in other provinces, such as Alberta and Saskatchewan.